It has long been known that many heart attacks (myocardial infarctions) are caused by clots forming in already partially obstructed coronary arteries secondary to atherosclerotic disease. At this point, time is of the greatest essence in trying to prevent permanent myocardial damage. Accordingly, while attempts have been made to inject substances which will lyse these clots and hopefully avert the myocardial infarction through direct catheterization of the small coronary arteries, their effectiveness has been limited due to the hours often necessary for the procedure together with the extensive equipment required and the intricate catheterization of the coronary arteries involved.